Lithium tantalite sintered body, method for producing same, and sputtering target using said sintered body
Patent Information
- Application Number
- PCT/JP2026/004936
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-27
- Filing Date
- 2026-02-12
- Publication Date
- 2026-10-01
Smart Images
Figure JPOXMLDOC01-APPB-T000001
Abstract
Description
Lithium tantalate sintered body, method for manufacturing the same, and sputtering target using the sintered body.
[0001] This disclosure relates to a lithium tantalate sintered body, a method for producing the same, and a sputtering target using the sintered body.
[0002] Lithium tantalate (LiTaO) ３ Single-crystal thin films of ) are widely used in piezoelectric materials and optical applications, and are particularly used in SAW (surface acoustic wave) filters. Conventionally, substrates sliced from single-crystal ingots have been used to form the thin films.
[0003] Regarding piezoelectric materials, Patent Documents 1 and 2 disclose niobate-based alkali piezoelectric / electrostrictive ceramic sintered bodies. Specifically, a sintered body having a tetragonal perovskite-type oxide as the main crystal is disclosed, containing at least one element selected from the group consisting of Li, Na, and K as an A-site constituent element, and at least one element selected from the group consisting of Nb and Ta as a B-site constituent element. Reference Document 3 describes a sputtering target for forming a dielectric film, wherein the oxygen-deficient LiTaO ３－ｘ Such ceramic materials are disclosed.
[0004] Japanese Patent Publication No. 2010-030810, Japanese Patent Publication No. 2010-053021, Japanese Patent Publication No. Hei 7-109566
[0005] As mentioned above, conventionally, substrates sliced from single-crystal ingots have been used to form thin films, but this method has limitations in terms of thin film thickness and poor yield. Therefore, there is a need for sintered bodies for sputtering targets that can improve yield and enable thin film formation.
[0006] It is known that the strength of sintered bodies produced by powder metallurgy improves as the crystal structure becomes finer (Hall-Petch's law). However, in the case of lithium tantalate sintered bodies, when the average crystal grain size is refined, a problem arises in that cracks occur during the processing of the sintered body.
[0007] In view of such problems, an object of the present disclosure is to provide a lithium tantalate sintered body in which the occurrence of cracking is suppressed, a method for producing the same, and a sputtering target using the sintered body.
[0008] The gist of the present disclosure is as follows. [1] A lithium tantalate sintered body containing Li, Ta and O, wherein the X-ray diffraction peak intensity ratio I ３ of trigonal LiTaO₃ (012) ＴＧ / I ＢＧ is 500 or more, and the average crystal grain size is 1.3 µm or more and 10 µm or less. [2] The lithium tantalate sintered body according to [1] above, which has a bulk density of 6.70 g / cm ３ or more. [3] The lithium tantalate sintered body according to [1] or [2] above, which has a volume resistivity of 10 kΩ·cm or more. [4] A sputtering target using the lithium tantalate sintered body according to any one of [1] to [3]. [5] Li ２ ₂CO ３ powder and Ta ２ ₂O ５ powder, calcining the mixed powder at 800°C or higher and 1100°C or lower to synthesize LiTaO ３ powder, and hot press sintering the synthesized powder at 1230°C or higher and 1350°C or lower in vacuum or an inert gas atmosphere, which is a method for producing a lithium tantalate sintered body.
[0009] According to the present disclosure, there can be provided a lithium tantalate sintered body in which the occurrence of cracking is suppressed, a method for producing the same, and a sputtering target using the sintered body.
[0010] Hereinafter, the present disclosure will be described with reference to specific embodiments, but each configuration and combinations thereof in each embodiment are merely examples, and addition, omission, replacement, and other modifications of the configuration can be appropriately made without departing from the gist of the present disclosure.
[0011] The lithium tantalate sintered body according to the embodiment of the present disclosure (also referred to as this embodiment) contains lithium (Li), tantalum (Ta), and oxygen (O). The content ratio of Li to Ta preferably satisfies the following formula. In the following formula, Li and Ta represent the atomic percentages of lithium and tantalum contained in the sintered body, respectively. 0.90 ≤ Li / Ta ≤ 1.20 (Formula) In the above formula, Li / Ta is more preferably 0.95 or more, and even more preferably 0.98 or more. Furthermore, Li / Ta is more preferably 1.10 or less, and even more preferably 1.05 or less.
[0012] The lithium tantalate sintered body according to this embodiment is trigonal LiTaO ３ The trigonal LiTaO ３ X-ray diffraction peak intensity ratio I of (012) ＴＧ / I ＢＧ The value is 500 or more. Trigonal LiTaO ３ Its crystal structure is relatively stable. Trigonal LiTaO ３ The X-ray diffraction peak intensity ratio of (012) is preferably 700 or more, and more preferably 800 or more.
[0013] Incidentally, the inventors conducted a microanalysis of sintered bodies that had cracked during processing and discovered that the cracks propagated through grain boundaries. Based on this, the inventors attempted to prevent cracking during processing of sintered bodies by adjusting the grain size of the sintered body to prevent a decrease in strength caused by grain boundaries.
[0014] The lithium tantalate sintered body according to this embodiment has an average grain size of 1.3 μm or more and 10 μm or less. If the average grain size is too small, cracks may occur during the processing of the sintered body. On the other hand, if the average grain size is too large, the strength of the sintered body will decrease, and cracks may occur during film formation on a sputtering target using the sintered body. The average grain size is preferably 1.4 μm or more. It is also preferably 7 μm or less.
[0015] The dimensional density of the lithium tantalate sintered body according to this embodiment is 6.70 g / cm³.３ The above is preferable. When a high-density sintered body is used as a sputtering target, it is expected to suppress the generation of particles during film formation. The dimensional density is preferably 7.00 g / cm³. ３ The above is more preferable, and more preferably 7.10 g / cm³. ３ That's all.
[0016] The lithium tantalate sintered body according to this embodiment preferably has a volume resistivity of 10 kΩ·cm or more. The higher the volume resistivity of the sputtering target made of the sintered body, the easier it is to control the film thickness, as low-speed film deposition by RF (Radio Frequency) sputtering becomes possible. The volume resistivity is preferably 50 kΩ·cm or more, and more preferably 100 kΩ·cm or more.
[0017] The lithium tantalate sintered body of this embodiment can be formed into a disc-shaped, rectangular, or cylindrical sputtering target by machining such as cutting, grinding, and polishing, and can be joined to a backing plate with a bonding material. The thickness of the sputtering target is preferably 20 mm or less, more preferably 3.0 to 15 mm, and even more preferably 6.0 to 12 mm. The surface area of the side to be sputtered is 81 cm². ２ It is preferable that the above conditions are met.
[0018] A lithium tantalate sintered body according to an embodiment of the present invention, and a method for manufacturing a sputtering target made using the sintered body, are described below. However, it is clear that the manufacturing conditions and the like are not limited to those disclosed below, and some omissions and modifications may be made. In order to avoid making the disclosed manufacturing method unnecessarily unclear, detailed explanations of well-known manufacturing processes and processing operations are omitted.
[0019] (1. Raw material powder) As raw material powder, Li ２ CO ３ Powder, Ta ２ O ５ Powder can be used. ２ O ５ Powder particle size D ５０The median diameter (by volume) is preferably 5 μm or less. More preferably 3 μm or less, and even more preferably 1 μm or less. ２ O ５ If the powder particle size is large, LiTaO may be produced in subsequent synthesis steps. ３ Since a single phase cannot be obtained, Ta with fine particle size ２ O ５ It is preferable to use powder. ２ O ５ Powder particle size D ５０ If the median diameter (by volume) is large, it is desirable to finely grind the raw material powder.
[0020] (2. Mixing process) Li ２ CO ３ Powder, Ta ２ O ５ Weigh the powder to achieve the desired composition ratio. Li ２ CO ３ Since the powder has hygroscopic properties, it is preferable to pre-dry it at 120°C for 12 hours or more before weighing. After weighing, these are mixed to obtain a mixed powder. In order to obtain a dense and uniform sintered body, fine grinding and uniform mixing may be thoroughly performed using a mixer such as a ball mill or attritor.
[0021] (3. Synthesis process) Li ２ CO ３ powder and Ta ２ O ５ The mixed powder is calcined in air at a temperature between 800°C and 1100°C to produce LiTaO ３ Synthesize the powder.
[0022] (4. Grinding process) After synthesis, the synthesized powder (LiTaO ３ The powder is dry-ground or wet-ground. Particle size D ５０ It is preferable to grind the material until the median diameter (by volume) is 1 μm or less. In the case of wet grinding, after weighing, the amount of media is determined according to the amount of raw material. The diameter of the media is 0.5 mm or 1.0 mm, and the material of the media is alumina (Al ２ O ３ ) and zirconia (ZrO ２) can be used. The dispersion medium is water or ethanol, and when water is used, it is preferable to recover the entire amount when taking out the mixed slurry. The grinding method is wet ball mill grinding or wet bead mill grinding, and the grinding time can be 1 hour or more. Using the grinding method described above, the particle size D ５０ It is preferable to mix and grind until the median diameter (by volume) is 1 μm or less. After wet grinding, the synthetic powder is dried, and then crushed and sieved.
[0023] (5. Sintering process) Synthetic powder (LiTaO ３ The powder is subjected to a vacuum or inert gas atmosphere at 200 kgf / cm². ２ The lithium niobate sintered body is produced by applying pressure as described above and hot-press sintering at a sintering holding temperature of 1230°C to 1350°C. If the sintering holding temperature is below 1230°C, the density of the sintered body may not increase sufficiently. On the other hand, if the sintering holding temperature exceeds 13500°C, the average grain size of the sintered body becomes coarser. The sintering time is preferably 1 hour to 10 hours. The heating rate is preferably 0.5 to 5°C / min.
[0024] (6. Finishing Process) The sintered body obtained through the above sintering process can be used to produce a sputtering target with a desired shape using a surface grinder, cylindrical grinder, machining center, or other processing machine as needed. The sputtering target is produced by machining the sintered body, and its relative density and flexural strength are substantially the same as those measured on the sintered body.
[0025] The following explanation is based on examples and comparative examples. However, these examples are merely illustrative and do not limit the invention in any way. That is, the present invention is limited only by the claims and encompasses various variations other than those included in the examples of this disclosure.
[0026] The evaluation methods used in the examples and comparative examples are as follows: (Compositional analysis) The composition of the sintered body was analyzed using the following apparatus: Apparatus: SPS3500DD manufactured by SII Corporation Method: ICP-OES (Inductively coupled plasma emission spectrometry)
[0027] (Regarding dimensional density) A sintered body was cut to a predetermined size (20 mm x 20 mm x 10 mm), its length, width, and thickness were measured, and its volume was calculated. The weight of the sintered body was also measured, and its dimensional density (g / cm³) was determined. ３ ) = weight / volume was calculated.
[0028] (Regarding average crystal grain size) An observation sample (15 mm x 15 mm x 5 mm) was cut from the sintered body, and the cross-section of the observation sample (the cross-section perpendicular to the surface facing the substrate that will be sputtered, in the case of processing into a sputtering target) was mirror-polished. Next, three fields of view were captured of the central part of the observation sample cross-section at a magnification of 1000 to 3000 times using the following scanning electron microscope. Note that the magnification may be changed as appropriate if the number of particles crossing each line in the field of view is less than 30.
[0029] Equipment used: JXA-8500F (manufactured by JEOL Ltd.) Acceleration voltage: 15.0 kV Beam current: 2.0 × 10⁻¹⁰ －９ A
[0030] Three straight lines (along the longer side of the image) were drawn on the captured image, and the length of each line and the number of crystal grains crossed by each line were determined. In this case, crystal grains whose ends were inside the line were counted as 0.5. Then, based on the measured lengths of the lines and the number of crystal grains crossed by each line, the crystal grain size in one field of view was calculated using the following formula: Crystal grain size in one field of view = (Length of line 1 / Number of crystal grains crossed by line 1 + Length of line 2 / Number of crystal grains crossed by line 2 + Length of line 3 / Number of crystal grains crossed by line 3) / 3
[0031] Then, the grain size was determined for each of the three fields of view using the above formula, and the arithmetic mean of these three fields of view was taken as the average grain size. In cases where there were many pores in the sintered structure, the average grain size was calculated from the length of the line drawn by subtracting the pore areas and the intersection point.
[0032] (Regarding volume resistivity) Volume resistivity was measured using the following equipment: Equipment: High Resistivity Meter High Resistar-UX MCP-HT800 manufactured by Nitto Seiko Analytech Method: Constant voltage application / leakage current measurement method Method: Double ring method Measurement temperature: Room temperature (20-25°C) Applied voltage: 10V The measurement was taken at the center of the diagonal of a sintered body processed into a square shape (thickness: 3-5 mm).
[0033] (Analysis of Crystalline Phase) The crystalline phase in the sintered body was analyzed using the following apparatus: Principle: X-ray diffraction apparatus: Rigaku Smart Lab tube: Cu-Kα ray tube Voltage: 40kV Current: 30mA Measurement method: 2θ-θ reflection method Scan speed: 20° / min Sampling interval: 0.02° Measurement range (2θ): 10° to 60° Divergence slit: 1° Divergence vertical limiting slit: 10mm Scattering slit: 8mm Receiving slit: Open Goniometer: Horizontal type Sample measurement location: Sputtered surface side
[0034] (LiTaO ３ (Analysis of crystalline phase) Trigonal LiTaO ３ The XRD peak intensity in the range of 23.0° ≤ 2θ ≤ 24.0° that belongs to (012) is I ＴＧ The average value of the XRD intensity in the range of 25.0° ≤ 2θ ≤ 26.0° is set to background I. ＢＧ As for trigonal LiTaO ３ X-ray diffraction peak intensity ratio I of (012) ＴＧ / I ＢＧ The result was calculated.
[0035] (Regarding the occurrence of cracks) If a crack of 3 mm or longer was observed by visual inspection of the surface of the sintered body (the surface corresponding to the sputtered surface), it was determined that "crack occurrence" had occurred.
[0036] (Example 1) Li ２ CO ３ Powder, Ta ２ O ５After weighing the powder such that Li:Ta = 1:1 (atomic percent), mixing was performed using a blade-rotation dry mixer. Thereafter, this mixed powder was calcined at 1000°C to obtain LiTaO ３ powder was synthesized. Next, the synthesized LiTaO ３ powder was finely pulverized to adjust the particle diameter D ５０ (volume-based median diameter) to 0.48 µm. After pulverization, LiTaO ３ powder was filled into a carbon die, and sintered under the conditions of Ar atmosphere, sintering holding temperature: 1250°C, pressure: 250 kgf / cm ２ , heating rate: 3°C / min for 5 hours to obtain a LiTaO ３ sintered body was produced. For the obtained LiTaO ３ sintered body, various physical properties were measured. As a result, the X-ray diffraction peak intensity ratio I of trigonal LiTaO ３ (012) plane I ＴＧ / I ＢＧ was 1968, the average crystal grain size was 2.47 µm, the dimensional density was 7.30 g / cm ３ , the volume resistivity was 3.10×10 ８ Ω·cm, and no occurrence of cracking was confirmed.
[0037] (Example 2) LiTaO produced by the same method as in Example 1 ３ powder was filled into a carbon die, and sintered under the conditions of Ar atmosphere, sintering holding temperature: 1250°C, pressure: 250 kgf / cm ２ , heating rate: 3°C / min for 3 hours to obtain LiTaO ３ sintered body was produced. For the obtained LiTaO ３ sintered body, various physical properties were measured. As a result, trigonal LiTaO ３ X-ray diffraction peak intensity ratio for (012) plane I ＴＧ / I ＢＧ was 983, the average crystal grain size was 1.50 µm, the dimensional density was 7.16 g / cm ３ , the volume resistivity was 8.91×10 ８ Ω·cm, and no occurrence of cracking was confirmed.
[0038] (Comparative Example 1) LiTaO produced by the same method as in Example 1 ３ powder was filled into a carbon die, in Ar atmosphere, sintering holding temperature: 1125°C, pressure: 250 kgf / cm２ , heating rate: 3°C / min, sintering for 5 hours to obtain LiTaO ３ sintered body was produced. For the obtained LiTaO ３ sintered body, various physical properties were measured. The results showed that trigonal LiTaO ３ (012) X-ray diffraction peak intensity ratio I ＴＧ / I ＢＧ was 883, the average crystal grain size was 0.72 μm, the dimensional density was 6.46 g / cm ３ , the volume resistivity was 4.39×10 ８ Ω·cm, and the occurrence of cracks was confirmed.
[0039] (Comparative Example 2) LiTaO produced by the same method as in Example 1 ３ powder was filled into a carbon die, and sintered under the conditions of Ar atmosphere, sintering holding temperature: 1250°C, pressure: 250 kgf / cm ２ , heating rate: 3°C / min for 5 hours to obtain LiTaO ３ sintered body was produced. For the obtained LiTaO ３ sintered body, various physical properties were measured. The results showed that trigonal LiTaO ３ (012) X-ray diffraction peak intensity ratio I ＴＧ / I ＢＧ was 1023, the average crystal grain size was 1.20 μm, the dimensional density was 7.12 g / cm ３ , the volume resistivity was 3.73×10 ８ Ω·cm, and the occurrence of cracks was confirmed.
[0040]
[0041] According to the present disclosure, a lithium tantalate sintered body with suppressed crack occurrence and a sputtering target can be obtained, which may contribute to the advancement of thin film formation technology by sputtering used in the manufacture of piezoelectric materials and optical devices. The present disclosure may contribute to Sustainable Development Goal (SDG) 9 led by the United Nations: "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."
[0042] According to this disclosure, lithium tantalate sintered bodies and sputtering targets can be obtained in which cracking is suppressed. Furthermore, thin films formed using the lithium tantalate sputtering target according to this disclosure are useful as piezoelectric materials and optical thin films.
Claims
1. Contains Li, Ta, and O, in a trigonal LiTaO crystal structure. ３ X-ray diffraction peak intensity ratio I of (012) ＴＧ / I ＢＧ A lithium tantalate sintered body having a coefficient of 500 or more and an average crystal grain size of 1.3 μm or more and 10 μm or less.
2. Dimensional density is 6.70 g / cm³ ３ The lithium tantalate sintered body according to claim 1 is as described above.
3. The lithium tantalate sintered body according to claim 1, wherein the volume resistivity is 10 kΩ·cm or more.
4. A sputtering target using a lithium tantalate sintered body according to any one of claims 1 to 3.
5. Li ２ CO ３ powder and Ta ２ O ５ powder, calcining the mixed powder at 800°C to 1100°C to obtain LiTaO ３ powder, and hot-press sintering the synthesized powder at 1230°C to 1350°C in vacuum or an inert gas atmosphere. A method for producing a lithium tantalate sintered body, comprising: